Your heart is leaking: the mechanics of mitral regurgitation

Science · Published 20 October 2026 · Updated 21 October 2026 Swipe more like this →

In short: Imagine a one-way door that fails to latch. In the heart, this happens when the mitral valve doesn't close fully, allowing blood to flow backward. While often mild and asymptomatic, this mechanical failure can eventually overwhelm the body's circulatory system, leading to heart failure or fluid buildup in the lungs.

Mitral regurgitation (MR) is a common valvular heart disease where blood leaks backward from the left ventricle into the left atrium during each heartbeat. In a healthy system, the mitral valve's leaflets close tightly to ensure blood moves in one direction. When they fail to seal, blood moves in two directions simultaneously. This backward flow increases pressure in the left atrium, which can eventually back up into the veins carrying blood from the lungs, potentially causing fluid to build up in the lungs and making it difficult to breathe.

The causes of this 'leak' are diverse. Primary MR stems from issues with the valve itself, such as mitral valve prolapse—where flaps bulge backward—or rheumatic fever, a complication of untreated strep throat. Secondary or functional MR occurs when other heart conditions, like cardiomyopathy (thickening of the heart muscle) or damage from a heart attack, pull the valve out of alignment. In some cases, the chordae tendineae—the tissue cords tethering the leaflets to the heart wall—can stretch or tear, causing sudden backward flow.

The progression of the disease varies significantly. Many people with chronic, compensated MR remain asymptomatic for years. However, as the heart works harder to pump blood against the leak, the left lower heart chamber may enlarge and the muscle may weaken, leading to congestive heart failure. Severe cases can trigger atrial fibrillation, an irregular heartbeat that increases the risk of blood clots and stroke. Treatment ranges from simple monitoring for mild cases to medications like ACE inhibitors and diuretics, or surgical repairs and replacements for severe damage.

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